Materials and processes for flotation of mineral substances

ABSTRACT

A froth flotation process for concentration cassiterite ore using certain polymers as gangue depressants, and the polymers themselves, are described. The polymers are water soluble acrylamide homopolymers or copolymers with acrylic or methacrylic acid or salts thereof.

United States Patent Griffith et al.

MATERIALS AND PROCESSES FOR FLOTATION OF MINERAL SUBSTANCES Inventors: Robert M. Griffith, Bradford;

Christopher Parkinson, Halifax, both of England Dec. 30, 1975 3,469,693 9/1969 Arbitel 209/166 3,572,504 3/1971 De Cuypel 209/166 FOREIGN PATENTS OR APPLICATIONS 861,579 10/1940 France 209/166 978,110 12/1964 United Kingdom 209/166 1,212,496 11/1970 United Kingdom 209/166 OTHER PUBLICATIONS Chem. Abst., 73, I970, p. 150, I01 l5ln.

Primary Examiner-Robert Halper Attorney, Agent, or Firm-Larson, Taylor and Hinds [57] ABSTRACT A froth flotation process for concentration cassiterite ore using certain polymers as gangue depressants, and the polymers themselves, are described. The polymers are water soluble acrylamide homopolymers or copolymers with acrylic or methacrylic acid or salts thereof.

7 Claims, No Drawings MATERIALS AND PROCESSES FCRFLO'ITATION,

or MINERAL SUBSTANCES v The use of the froth flotation process for thebeneficiation, or concentration, of mineral ores is very well known. The object of the process usually is to produce a concentrate of a certain mineral substance from the crude ore in which the required mineral substance is diluted by the presence of other minerals which are unavoidably extracted with it in the mining operation. The overall process of concentrating an ore comprises forming an aqueous pulp of the ore by first grinding the crude ore to such an extent that discrete particles of the required mineral occur, and then subjecting the pulp to froth flotation. Generally it comprises subjecting the pulp to agitation in the presence of rising air bubbles.

To assist the process a chemical substance known as a collector" is incorporated into the mass and by virtue of its chemical and physical properties this collector will selectively adsorb onto one or more of the minerals present in such a way that these minerals, in

preference to the other minerals, become attached to the air bubbles. In this way the preferred minerals rise to the surface of the aqueous mass from whence they can be collected and a degree of mineral separation is thus brought about. In some 'cases the gangue or unwanted minerals are caused to float preferentially in this way, but more commonly the valuable minerals are floated and collected as a concentrate.

Complete selectivity with regard to separation of the minerals is difficult to achieve and frequently several sequential flotations are required before an adequate degree of ore refinement is obtained. Those flotations carried out on the crude ore are often referred to as rougher" operations and reflotations of the rougher concentrates are often referred to as cleaner operations.

It is well known to add other chemical reagents to improve the selectivity of the flotation process, amongst which are substances which are termed depressants because of their general effect on the process which is to make the unwanted minerals less likely to be floated simultaneously with those which are required to be floated. The manner in which these modifying agents achieve their effect is not known with certainty and various theories have been offered as to their mode of action. It is possible that some of these materials act by preferential adsorption onto the surface of the unwanted material and in consequence could reduce the state of flocculation of these minerals or increase their hydrophilic properties, both of which would give them less tendency to adhere to the air bubbles, or they may prevent the associated minerals from adhering to the required minerals, or they may prevent the collector from adsorbing onto the associated minerals or other mechanisms may be operative. Whatever the mechanism the utilisation of a depressant" can have a valuable effect on the economics of the flotation process. A very wide variety of mineral .for example, those of tungsten, manganese, barites,

substances can be beneficiated'by froth flotation. Naturally the surface properties of different mineral substances can differ greatly..As a result depressants tend to have a very high degree of specificity. In practice therefore a depressant that is very useful on onemineral substance often has little or no useful depressant effect on another. Accordingly mere disclosure that a material is a depressant in froth flotation processes givesno useful guide as to whether that material will be a useful depressant in the flotationof any particular.

Synthetic polymers have also -been disclosed as de-- pressants and again a high degree of specificity exists. 0 A veryearly disclosure of the use of synthetic polymers as depressants is in British specification No. 749,213. Thus .it is allegedthere that froth flotation of ore'sis greatly improved when a water soluble anioniclinear addition polymer of a monoethylenically unsaturated compound, having an average molecular weight of at least 10,000, is used as depressant. A very wide variety of ores and a large number of different polymers are disclosed. Thus it is stated that the invention is applicable to gangue slimes of the most varied types of ores such as siliceous gangue present in metallic or sulphide ores, for example, lead, zinc, copper, pyrites, lead-zinc ores, precious metal ores. It is also applicable to the various gangues present in non-sulphide ores such as,

fluorspar, limestone and phosphate rock. Talcs, mica s, clays, sericite, liminotes, fibre carbon and on occasion fine calcite are examples of gangues which interfere with. flotation especially when these-are present as slimes, and other minerals when in the form of slimes frequently are harmful. Further it is stated that among the polymers that can be used in the invention are hydrolysed polyacrylonitrile, polyacrylamide, polyacrylic acid, one-half calcium salt of hydrolysed ,l:l copolymer of vinyl acetate-maleic anhydride, hydrolysed styrene-maleic anhydride copolymer, ammonium polyacrylate, sodium polyacrylate, ammonium polymethacrylate, sodium polymethacrylate, diethanol ammonium polyacrylate, guanidinium polyacrylate, dimethylaminoethyl polymethacrylate, acrylamideacrylonitrile vcopolymer, methacrylic acid-dime thylaminoethyl methacrylate copolymer, sodium salt of acrylic acid-vinyl alcohol copolymer, hydrolysed methacrylic acid-acrylonitrile copolymer, vinyl acetatemaleic anhydride copolymer, vinyl formate-maleic anhydride copolymer, vinyl methyl ether-maleic anhydride copolymer, isobutylene-maleic anhydride copolymer, styrene-maleic anhydride copolymer, ethyl acrylate-maleic anhydride copolymer, vinyl chloride-maleic anhydride copolymer, hydrolysed acrylonitrile-vinyl acetate copolymer, hydrolysed acrylonitrile-methacrylonitrile copolymer, hydrolysed acrylonitrile-methacrylonitrile-vinyl acetate terpolymer, hydrolysed acrylonitrile-methacrylic acid copolymer, vinyl pyridine-acrylonitrile copolymer. The preferred polymers are said to be hydrolysed polyacrylonitrile. I

In view of the high specificity of action of synthetic polymers as depressants it is perhaps rather unlikely that really useful results will be achieved with the many hundreds of theoretically possible combinations of disclosed ores and disclosed polymer types. Indeed most literature on the use of synthetic polymers is very much more specific. Thus South African Pat. No. 67/2678 and French Pat. No. l,5l9,540 describe the use of low molecular weight polymers of acrylic acid as depressants in the flotation of copper minerals in the presence of calcareous and dolomitic gangues. U.S.S.R. Pat. Nos. 130,428 and 141,826 also describe the use of polyacrylic acid in the beneficiation' of vari- 3 ous metaliferous ores. U.S.S.R. Pat. No.- 144,124 describes the use of polymers containing acrylamide and ethylene sulphonate in the beneficiation of sulphide ores.

Several patents, including East German Pat. No. 21 ,241, French. Pat. No. 1,412,963, US. Pat. Nos. 3,282,418,-3,310,170 and 3 ,452,867, German Pat. No. 1,267,631, and U.S.S.R. Pat. No. 160,476, describe the use of acrylic polymers in the beneficiation of potassiumsalts. German specification No. 1,267,631 makes generic disclosures of polymers containing up to 80 percent polyacrylamide fordepressants effective in the flotation of potassiur'n'salts. The presentinvention relates to the concentration of cassiterite ore. This ore comprises cassiterite, a naturally occurring mineral comprising stannic oxide together with many impurities, generally including siliceous materials. Despite the commercial importance of cassiterite as a source of tin it is not mentioned in British specification No. 749,213 or any of the'other specifications mentioned above. However there has been a considerable amount of research done into the flotation of cassiterite ore. British Pat. No. 1,110,643 and German Pat. No. 2,157,262 describe the flotation of cassiterite by a process in which sulphosuccinamatesv are used as'collectors. British Pat. No. 978,110 describes a flotation process for cassiterite using phosphonic acids, in particular para-tolyl phosph'onic acid. Para-tolyl arsenic acid is also well known as a collector for cassiterite ore flotation. I

It has been our object to provide a flotation process for the concentration of cassiterite ore using a depressant such that improved results are obtained over those obtainable in prior processes for the flotation of cassiterite ore.

According to 'the invention we subject an aqueous pulp of cassiterite ore to a froth flotation process in the presence of both a colletor and a gangue depressant and we use as the gangue depressant a water soluble polymer containing 40 to 100 mole percent recurring groups A and to 60 mole percent recurring groups B, the mole percentages being based on A+B, where A represents ea l-land B represents and/or R being methyl or, preferably, hydrogen, and having a can also be used and is often preferred, suitable copolyme'rs'containing-40 'to 98 inole percent'A and 2 to 60 mole percent B.- Best'results are generally obtained with copolymers containing to 95 mole percent A and 5 to 30 mole percent B. In particular copolymers containing from between or mole percent A up to or mole percent A are generally very satisfactory. v

' it is usually preferred that the homopolymers or copolymers consist solely of groups A and B but other groups may be included in small amounts,e.g., up to 10 mole percent based on A+B as diluents without serious deleterious effects. The groups B, if present, may either be acrylic and/or methacrylic acid groups or some or all of them may be in the form of salts with cations that give a water soluble salt. Suitable cations are sodium or other alkali metals or ammonium. The copolymers may be added-to the pulp of the ore either in the acid form or as a water soluble salt, but the pH at which flotation is carried out willdetermine whether the polymer is present as the acid or as the salt, or at certain pH values, as a mixture of the two. i

We preferto specify the molecular weight of the polymers we use in terms of the viscosity of their solu tions. The polymers are such that aqueous solutions containing 10 percent'by weight of the polymer have a viscosity in centipoise (measured at 25C, at a pH of 7.0, in the absence of added salt's, using a Brookfield Model RVT viscometer at a spindle'speed of 20 rpm) of between 8 (No. l spindle) and 50,000 (No. 6 spindle). Viscosities at this concentration of between l5 (No. 1 spindle) and 5,000 (No. 5 spindle) are'particularly advantageous and a viscosity of between 25 (No. l spindle) and 300(No. 2 spindle) is especially preferred.

The polymers may all be made using any of the well known polymerisation methods involving standard techniques of controlling the molecular weight. Thus they may all be made by polymerisation in an aqueous. solution of the monomers using free radical or redox initiators such as hydrogen peroxide or ammonium persulphate and controllingthe molecular weight either by varying the initiator concentration or by, addition of well known chain transfer reagents such as alcohols or thiols.

The use of the polymers in the invention gives goodresults at very economical dosage levels, and for instance, good results have been obtained at a dose corresponding to about 25 g. of the polymer to 1 ton of ore feed. I

The froth flotation of the-present invention may be carried out in accordance with good flotation practice and critical or unusual techniques are not necessary. The exact conditions under which best results may be obtained will depend on the exact:nature of the ore being treated. 1n general any mechanical flotation machine may be employed, or air cells may be used.

It is necessary to use in the process a collector by which we mean thata collector is used at a dose and under conditions of,-for example, pH and metal ion concentrations such that cassiterite can be floated evenin the absenceof depressant. Any suitable collectors useful for collecting cassiterite may beused for example aryl (e.g., para-tolyl) arsonic-acid,--aryl (e.g., paratolyl) phosphonic acid and alkyl succinamates, as described in British Pat. No. 1,110,643 or German Pat. No. 2,157,262.

the grade of the cassiterite concentrate. The use of an excessive amount of the depressant usually leads to a decrease in the recovery of cassiterite. Generally a dosage of between and 250 gm of'polymer per tonne of feed solids should prove to be jsufficient to -give greatly enhanced grades of cassiterite concentrate.

Conventional frothers may be used, methyl isobutyl carbinol being found advantageous in some cases, although in other cases the collector alone'may provide sufficient froth.

The froth flotation of the present invention usually though not always involves flotation in rougher cells, followed by one or more cleanings of the rougher concentrate. It is possible to carry out rougher and cleaner flotations with single additions of collecting 6 in a. manner such that the polymer may readily be dispersed'throughoutthe slurry.

The following examples illustrate the invention:

EXAMPLE 1 The flotation feed was a finely disseminated complex was agitated for 3 minutes following each addition of collector and the polymeric depressant in aqueous and depressing reagents at the beginning of the operation, although in some cases it has been found advantageous to add the depressant to the pulp after the addition of collector. Thus an advantageous procedure may be to add the major amount of collector at'the rougher stage, and add the depressant at the subsequent cleaning stages. On the other hand it may be advantageous to use additions of collecting and depressing reagents at each flotation stage. The exact reagent additions at each stage will depend on the-grade of the ore and .the associated minerals. Pulp densities are in general the same as in other applications of froth flotation, for example between about 15 to 45 percent-of solids by 1st Rougher Concentrate 2nd Rougher Concentrate 3rd Rougher Concentrate TAIL This figure represents the recovery of tin at each stage.

weight.

Whilst it is practical, and in most operations preferable, to float with the polymeric depressants of the present invention as the only depressants, it is also possible to use them in conjunction with other depressants, such as the known depressants including, e.g., soluble silicates and fluosilicates. A

As in conventional flotation practice, the naturalore being beneficiated is usually first ground to liberation mesh" size and slurried with water to form the pulp. The collector is added in water solution to the slurred viscometer (No. 2 spindle, 20 rpm) of about 250 centipoise. The polymeric depressant was added following each of the three. collector additions, at doses of .100 gm/ton, gm/ton and 50 gm/ton. Approximately 40 gm/ton. methyl isobutyl carbinol frother was added at the first and third stages of flotation. The results were as follows:

% Weight of Tin Assay Tin Floated Distribution* Concentrate EXAMPLE 2 gm/ton of collector; The pulp was agitated for a further 3 minutes before flotation was commenced. Two further collector additions of gm/ton were made as in Example 1, but no further depressant was added. The results were as follows:

% Weight of Tin Assay Tin Floated Distribution Concentrate 1st Rougher Concentrate 14.6 4.0% 66.4% 2nd Rougher Concentrate 4.4 2.5% 12.7% 3rd Rougher Concentrate .3 0.9% 15.6% TAIL 65.7 0.07% 5.3%

ore whilst the ore is agitated. The polymeric depressant may then advantageously be added in water solution to the agitated slurry and after a short time the slurry may be treated by conventional methods of froth flotation. The polymeric depressant should be added to the slurry 1st Rougher Concentrate 2nd Rougher Concentrate 3rd Rougher Concentrate As a control, the same procedure was carried out on an identical sample of ore omitting only the depressant additions and the subsequent 3 minute conditioning periods with the following results:

% Weight of Tin Assay Tin Floated Distribution Concentrate 34.7 1.8% 69.9% 5.1 1.1% 6.2% 12.1 1.0% 13.6% TAILS 48.1 0.19% 10.3%

These xamplesshow that with use of thepre'ferre'd polymeric depressants of the invention tin assay of the rougher concentrate" may be improved from-below 2 percent in the control test, to 3.8. percent and above in the tests using polymeric depressants. Additionally the amount of tin' recovered at these higherassays may be greater when the depressants are used.

A series of tests was carried out using feed identical to that of Example'siland 2 and using the same procedure as ExampleI 'fZ but using differentpolymeric de- 10 The first two concentrates taken together have a tin assay of 3.0 percent.

' EXAMPLE (COMPARISON) p s n gm/ton with the following results:

% Weight of Tin Assay Tin Floated Distribution Concentrate 1st Rougher Concentrate 18.6 1 1.3% 23.5% 2nd Rougher Concentrate 6.9 4.6% 30.6% 3rd Rougher Concentrate 18.6 1.6% 29.0% TAILS 55.9 0.31% 16.9%

, ,EXAMPLE 3. a

Theflotation feed and procedure was the same as Example 2. The polymeric depressantu's ed was ahomopolymer of acrylamide having a viscosity in aqueous solution at percent solids (by weight), at C, at a pH of 7.0-, using'a Brookfield viscometer (No. 1 spindle) at 20 rpm,of'- about centipoise; Such a viscosity is characteristic of a polymer having an-average molecular weight of between 25,000 and 250,000. The polymer was used at a dose of 150 gm/ton with the following results: r

The first two concentrates taken together have a tin assay'of 2.2 percent.

EXAMPLE 6 5 A flotation feed similar to that of Example 1 was 30 and 200 gm/ton respectively. The collector was dissolved in dilute sodium hydroxide. The flotation pulp was agitated for 3 minutes following each addition of Weight of Tin Assay Tin I Floated Distribution Concentrate 1st Rougher Concentrate 19 8 3.6% 74.4% 2nd Rougher Concentrate 5.2 1.4% 7.6% 3rd Rougher Concentrate 18.3 0.6% 11.5% TAILS 56.7 .l 1% 6.5%

EXAMPLE 4 collector e polymeric depressant of Example was Usingagcopolymer of acrylic acidand acrylamide in the ratio 2 :3: and having a Brookfield viscosity at pH of 2 in aqueous solution at 25 percent solids of about 21,000 centipoise (25 rpm spindle .6). Suchaviscosity added at a dose of gm/ton before the first addition of collector, and a 3 minute conditioning period was al- 5 lowed. Approximately 40 gm/ton methyl isobutyl carbinol frother was added at the first stage of flotation. The results were as follows:

is characteristic of a polymer having an average molecular weight of between 200,000 and ,2,000,000. The

As a control the procedure was repeated, omitting only the depressant addition with the following results:

polymer was used .at a dose of gm/to n with the 0 following results: v

% Weight of Tin Assay Floated Distribution Concentrate 1st Rougher Concentrate 14.2 2.7% 36.0% 2nd Rougher Concentrate 6.4, 3.8% 22.7% 3rd Rougher Concentrate 18.5 1.6% i v 27.6% TAILS 60.9 0.24% 13.7%

% Weight of Tin Assay Tin I Floated Distribution Concentrate 1st Rougher Concentrate 17.1 2.7% 39.7% 2nd Rougher Concentrate 13.8 2.6% 31.0% l 3rd Rougher Concentrate 8.4 1.8% 12.1%

TAILS 60.7 0.23% I 17.2%

EXAMPLE 7 0 EXAMPLE 9 (COMPARISON) A flotation feed similar'to that of Example 1 was treated using a laboratory Wemco flotation cell and using as collector a commercially available grade of para-tolyl-arsonic acid containing 13.1 percent Arsenic. The pH of the .pulp was maintained at 6.0.and the method of Example 2 was employed using the colle ctor at doses of 2 kgm/ton, 1 kgm/ton and l kgm/ton, and using the polymeric depressant of Example 1 at a dose of 25 gm/ton.

A further test was carried out using a sample of ore identical to' that of Example 7, and using the same procedure but using as depressanta commercially availablesalt of hydrolysed polyacrylonitrile having a suspended level viscosity of 250 centistokes, measured at a pH of l 1.0'in' aqueous solution at a 1 percent solids concentration. Such a 'viscosity is characteristic of a polymer having an average molecular weight of between 1,000,000 and 10,000,000. The poly'mer'was The following results were obtained: used dissolved in water at a dose of gm/ton with the Weight of Tin Assay Tin Floated Distribution Concentrate I lst Rougher Concentrate 15.6 2.5% 72.3% 2nd Rougher. Concentrate 7.6 1.3% 18.1% 3rd Rougher Concentrate 17.2 0.3% 9.6%

TAILS I 59.6

As a control the same procedure was carried "out following results:

% Weight of using an identical sample of ore, omitting only the depressant addition and the subsequent 3 minute conditioning period with the following results:

The tests in Example 2 and Example 7 demonstrate that the addition of the specified polymers of the invention as depressant gives markedly improved results Weight of Tin Assay Tin Floated Distribution Concentrate 1st Rougher Concentrate 35.1 1.5% 89.5% 2nd Rougher Concentrate 9.0 0.5% 7.8% 3rd Rougher Concentrate 8.0 0.2% 2.7%

TAILS 47.9

EXAMPLE 8 (COMPARISON) compared to flotation processes in which no depressant is used. Comparison of Examples 3, 4 and 5 shows that the ratio of AB is an important factor. Thus the copolymer of Example 4, containing 40 mole percent acrylic acid, is very much better than polyacrylic acid homopolymer (which is disclosed in British specification No. 749,213) and indeed the polyacrylic acid gives a very poor result. The polymer of Example 2, containing 20 mole percent acrylic acid, gives a primary concentrate grade better than that when polyacrylamide homopolymer is used, as in Example 3. Thus it appears that the copolymer ratio for maximum effectiveness is approximately 20 mole percent acrylic acid with Weight of Tin Assay Tin Floated Distribution Concentrate 1st Rougher Concentrate 22.1 1.9% 74.9% 2nd Rougher Concentrate 12.1 0.8% 17.5% 3rd Rougher Concentrate 14.2 0.3% 7.6%

TAILS 51.5

mole percent acrylamide, effectiveness falling off on either side of this. The importance of the copolymer ratio is shown again by comparison of Examples 7 and 8 in that although the copolymer of Example 8 (as,

specified in German Pat. No. 1,267,631) gives a slight improvement in primary concentrate grade compared to when no depressant is used, the improvement is much less than thatobtained in Example 7, when the depressant isa polymer of theinvention. This again demonstrates the high specificity of polymers as depressants in the flotation of minerals. Finally, comparison of Example 9 with Example 7 shows that the results obtained when hydrolysed polyacrylonitrile is used are very inferior to those when a polymeric depressant according to the invention is used. Hydrolysed polyacrylonitrile was stated in specification No. 749,213 to be the preferredfpolymeric depressant and yet from these re'sults it is self evide'nt that far from being preferred it is in fact very poor indeed when applied to cassiterite. This demonstrates again the high degree of specificity there is in the action of a polymer as a depressant, a polymer that may be a good depressant for one ore, or even for several ores, being very poor on another type of mineral, for example cassiterite ore.

We claim:

1. A method of concentrating cassiterite ore by subjecting an aqueous pulp of the ore to a froth flotation process in the presence of a collector and a gangue depressant, in which process the gangue depressant is a water soluble polymer containing from 40 to 100 mole percent recurring groups A and to 60 mole percent recurring groups B, the mole percent beingbased on A-l-B, where A represents I -cH,- H-

12 and B represents ,CH, R

and/0r wherein R is hydrogen or methyl the polymer having a molecular weight distribution such that a solution'of the polymer in water containing 10 percent by weight a of the polymer has at pH 7 and a temperature of 25C a Brookfield viscosity of between 8 and 50,000'centipoise. 1

2. A method according to claim 1 in which the depressant is a copolymer of 40 to 98 mole percent A and 2 to 60 mole percent B, the percentages being based on A+B.

3. A method according to claim 2 in which the copolymer contains to mole percent A and 5 to 30 mole percent B, the percentages being basedon A+B.

4. A method according to claim 1 in which the cosuccinamate. 

1. A METHOD OF CONCENTRATING CASSITERITE ORE BY SUBJECTING AN AQUEOUS PULP OF THE ORE TO A FROTH FLOTATION PROCESS IN THE PRESENCE OF A COLLECTOR AND A GANGUE DEPRESSANT, IN WHICH PROCESS THE GANGUE DEPRESSANT IS A WATER SOLUBLE POLYMER CONTAINING FROM 40 TO 100 MOLE PERCENT RECURRING GROUPS A AND 0 TO 60 MOLE PERCENT RECURRING GROUPS B, THE MOLE PERCENT BEING BASED ON A+B, WHERE A REPRESENTS
 2. A method according to claim 1 in which the depressant is a copolymer of 40 to 98 mole percent A and 2 to 60 mole percent B, the percentages being based on A+B.
 3. A method according to claim 2 in which the copolymer contains 70 to 95 mole percent A and 5 to 30 mole percent B, the percentages being based on A+B.
 4. A method according to claim 1 in which the copolymer consists of groups A or A and B.
 5. A method according to claim 1 in which the molecular weight of the polymer is such that an aqueous solution containing 10 percent by weight of the polymer has at pH 7 and a temperature of 25*C a Brookfield viscosity of from 15 to 5,000 centipoise.
 6. A method according to claim 1 in which R represents hydrogen.
 7. A method according to claim 1 in which the collector is an aryl arsonic acid, aryl phosphonic acid or alkyl succinamate. 